Multi-stage model rocket assembly

ABSTRACT

RELIABLE SEQUENTIAL IGNITION OF SUCCESSIVE ENGINES IN A MULTI-STAGE MODEL ROCKET IS ACHIEVED BY RELEASABLY POSITIONING SUCCESSIVE ENGINES IN END-TO-END RELATIONSHIP AND BY COUPLING EITHER THE ENGINES OR TUBULAR SHELLS CONTAINING THE ENGINES WITH A COUPLER RING HAVING HOLES SIZED TO VENT THE PRESSURE FRONT FORMED WHEN THE PRECEDING ENGINE BURNS TO ITS LEADING END TO DELAY SEPARATION OF THE ENGINES UNTIL THE NEXT ENGINE IGNITES AT ITS DISCHARGE END.

March 20, 1973 1.. E. PIESTER 3,721,193

MULTI-STAGE MODEL ROCKET ASSEMBLY Filed larch 25, 1970 INVENTOR. LEROY E. PIESTER ROBERT E. ROYAL @M ZK; gig 4 a.

ATTORNEYS United States Patent C) 3,721,193 MULTI-STAGE MODEL ROCKET ASSEMBLY Leroy E. Piester and Robert E. Royal, Phoenix, Ariz., assignors to Centuri Engineering Company, Inc. Filed Mar. 25, 1970, Ser. No. 22,617 Int. Cl. F24b 13/28, 15/14 US. Cl. 102-345 1 Claim ABSTRACT OF THE DISCLOSURE This invention relates to model rockets.

More particularly, the invention concerns multi-stage model rocket assemblies in which the reliability of sequential ignition of each successive engine is improved.

Even more particularly, the invention concerns improvements in multi-stage model rocket engine assemblies in which the pressure front formed when a preceding engine burns to its leading end is vented to delay separation of the engines and their respective stages until ignition of the next-succeeding engine occurs, thereby improving the reliability of the sequential ignition of the several engines.

In recent years, the sport and hobby of model rock'etry has gained significant popularity. In the later stages of the development of model rocketry, interest has shifted toward more complex models, and today the so-called multi-stage model rocket is of prime importance. These multi-stage model rockets function in a manner analogous to the full-sized multi-stage rockets used in military and scientific endeavors. In both the full-sized and model rockets, the rocket is constructed of two or more stages, each provided with an engine which upon ignition propels its stage and those stages above it until its fuel supply is exhausted, at which time the burned out lower stage is separated and the engine in the next stage is ignited.

Because model rockets are smaller and because it is desired to reduce the cost and complexity of model rockets to the point that the general population, especially children, can afford to, and have sufficient technical expertise, to purchase and operate them, the method for achieving sequential ignition of the engines in multistage model rockets must, perforce, be technically simple and economical.

The general method of obtaining sequential ignition in multi-stage model rockets is to use hot combustion products produced by burning the propellant charge in a preceding stage to ignite the propellant of the engine in the next-succeeding stage. For example, this general tech nique of obtaining sequential ignition in a multi-stage model rocket is disclosed in U18. Pat. No. 3,292,302.

Probably the most reliable method yet devised for achieving sequential ignition of the successive engines of a multi-stage model rocket involves securing the engines together in end-to-end alignment by means of a piece of adhesive tape wrapped circumferentially around the adjacent ends of the engines. Although this method increases the reliability of ignition appreciably .as compared to assemblies in which the engines are not secured by the adhesive tape, there still exists a substantial problem of obtaining reliable sequential ignition.

The principal reason for sequential ignition failures,

Patented Mar. 20, 1973 even though the adhesive tape method is employed to secure the engines, is that a pressure front or wave is formed when the rear or preceding engine burns to its leading end to the point that combustion products are emitted into the discharge end of the succeeding engine. This pressure front or wave tends to force the engines apart, possibly even to the extent of causing stage separation, and in a number of instances this separation of the engines takes place before a sufiicient quantity of combustion products have been emitted into the discharge end of the next engine to cause it to ignite.

Accordingly, it would'be highly advantageous to provide means for improving reliability of sequential ignition of multistage model rocket engines, which means funcltion simply and economically to provide this desired resu t.

It is therefore a principal object of the invention to provide an improved multi-stage model rocket assembly.

Another object of the invention is to provide an improved multi-stage model rocket engine assembly in which reliability of sequential ignition of the engines is increased.

Still another object of the invention is to provide a model rocket asembly which is simple, economical to construct and which can be purchased and operated by persons of limited economic means and/or technical expertise.

These and other, further, and more specific objects and advantages of the invention will become apparent to those skilled in the art from the following detailed description taken in conjunction with the drawings, in which:

FIG. 1 is an external perspective view of a multistage model rocket assembly;

FIG. 2 is a sectional perspective view of a multistage rocket such as that illustrated in FIG. 1, embodying principles and features of the present invention; and

FIG. 3 is a sectional perspective view of a pair of model rocket engines positioned in operative end-to-end aligned relationship and illustrating another technique for achieving the objects of the invention.

Briefly, in accordance with our invention, we provide improvements in a conventional assembly of model rocket engines for a multi-stage model rocket. In such conventional assembly, each engine which has a leading end and a discharge end is disposed within a respective stage of the rocket in end-to-end relationship with at least one other engine such that the leading end of the preceding engine is disposed proximate the discharge end of the next succeeding engine. Each succeeding engine is adapted for sequential ignition in its discharge end by combustion products emitted from the leading end of the preceding engine at the time the preceding engine burns to its leading end.

Our improvements specially adapt the above-described assembly to achieve reliable sequential ignition of each said succeeding engine before separation of the preceding stage of the rocket. Our improvements comprise the combination of means for releasably positioning at least two of the rocket engines in the required end-to-end adjacent relationship and means for venting the initial pressure front formed when the preecding rocket engine burns to its leading end, thereby delaying separation of the engines until the next-succeeding engine ignites at its discharge end, causing a sudden further pressure rise which is sufficient to separate the engines.

In a presently preferred embodiment of the invention, the means for releasably positioning the engines comprise tubular shells, one for each of the engines, sized to accommodate an engine by means of a slip fit therewithin and means for securing the shells together to position the engines in the required end-to-end adjacent relationship.

In this preferred embodiment, the means for venting the pressure front comprise an annular engine coupler which is sized to accommodate the adjacent ends of the tubular engine shells inserted therewithin. The annular engine coupler functions to releasably hold the tubular engine shells in adjacent relationship by frictional engagement between the outer surface of the engine shells and the inner surface of the annular coupler. The annular engine coupler is provided with ports in its wall. These ports are sized to vent the initial pressure front established by the burning of the preceding engine to its leading end, delaying separation of the engine until sequential ignition of the next-succeeeding engine is accomplished, causing a further pressure rise between the engines which results in separation of the tubular shells by overcoming the frictional engagement between the shells'and the engine coupler.

Depending upon the particular details of construction of the multi-stage model rocket, it may be necessary that the annular egine coupler frictionally engage the outer cylindrical surface of the ends of the adjacent engines rather than the outer surfaces of adjacent engine shells as described above. This variation provides the same result, namely, delay of the separation of the engines until sequential ignition is reliably accomplished, whereupon the subsequent pressure generated by ignition of the next engine overcomes the frictional engagement between the engine coupler and the ends of the adjacent engine casings.

Turning now to the drawings in which the presently preferred embodiments of the invention are depicted for purposes of illustration, FIG. 1 is a perspective view of a multi-stage model rocket assembly which can incorporate the features of the present invention. The multi-stage rocket usually comprises a nose cone 1, an upper-stage or auxiliary body section 2, and a lower-stage or main body section 3. Each stage is provided with approximate stabilizing fins 2a and 3a as required in order to provide thte proper flight dynamic characteristics. As will be apparent to those skilled in the art, it is within the contem plation of the present invention that the rnulti-stage model rocket can include more than the two stages shown in FIG. 1 and, for example, might include three or possibly more stages. However, in general it can be stated that the multi-stage rocket will always include a lower, or main, stage such as indicated by reference character 3, one or more upper, or auxiliary, stages such as indicated by reference character 2, and may or may not contain a separate nose cone or other payload section.

The principles of the present invention are further illustrated in FIG. 2 which is a perspective, cutaway, sectional drawing which illustrates the general internal arrangement of parts of a multi-stage rocket such as that illustrated in FIG. 1. As shown in FIG. 2, the lower stage, generally indicated by reference character 3, comprises an outer rocket body shell 21, an inner engine mounting shell 22 and annular spacing members 23 and 24 which position the inner engine shell 22 in proper concentric position within the outer shell 21.

Likewise, the auxiliary body sections forming the upper stages of the rocket assembly comprise an outer rocket body 25 and an inner tubular engine shell 26 positioned in concentric relationship by means of spacing rings 27 and 28. The various stages of the rocket can be coupled by means of a coupling member 29 frictionally engaging the inner surfaces of the outer rocket body sections 25 and 21 at their adjacent ends. Alternatively, the stages could be coupled by means of frictional engagement between male and female portions formed in the adjacent ends of the outer rocket body sections 21 and 25.

In a preferred embodiment, the model rocket engines are received and slip fit within the inner tubular engine shells 22 and 26 which are in turn frictionally engaged within an annular coupler 30 provided with ports 31. The ports 31 are sized and spaced in any suitable arrangement in such manner as to vent an initial pressure front caused by the burning of the lower engine to its leading end until ignition of the upper engine at its discharge end is accomplished. Ignition of the upper engine causes a second and much more marked increase in pressure at the junction of the adjacent tubular engine shells 22 and 26 which is sufficient to overcome the frictional engage ment between the adjacent ends and the engine coupler 30. As Will be appreciated, additional upper or auxiliary stages, as generally indicated by reference character 2, can be added to the assembly of FIG. 2 to provide model rocket assemblies having three or even more stages.

FIG. 3 illustrates a typical engine assembly which can be effectively employed in accordance with the present invention in a two-stage model rocket. The assembly includes the lower, or so-called booster engine,

' generally indicated by reference character A, and the upper, or so-called ejection charge engine, generally indicated by reference character B. In the case of a multi-stage rocket having more than two stages, additional booster engines A would be included in the assembly by coupling them in end-to-end relationship with the booster engine A.

FIG. 3 also illustrates another embodiment of the invention which might be employed in the event the engines are positioned within the rocket body by means other than the spacing rings and tubular engine shells illustrated in FIG. 2 as, for example, by means of frictionally engaging the engines themselves within the rocket body in the manner generally illustrated in US. Pat. No. 3,292,302. In this variation, an annular engine coupler 32 frictionally engages the adjacent ends 33 and 34 of the engines A and B, which coupler is provided with properly sized holes 32a for venting the initial pressure front.

As shown, the booster engine typically comprises an engine casing 35, usually fabricated of cardboard or other suitable material, a heat-resistant nozzle 36 carried in the discharge end 37 of the engine, and a solid propellant powder charge 38 formed within the casing 35 above the nozzle 36. This engine can be effectively and reliably ignited by means of various igniting mechanisms such as electrically heated wires or, in the case of a three or more stage rocket, ignition can be accomplished by means of hot combustion products emitted within the nozzle cavity 39.

In a typical multi-stage rocket, the uppermost engine will include the usual engine casing 41 and heat-resistant nozzle 42. However, the upper stage, or so-called sustainer engine, will usually contain in addition tothe propellant charge 43 a time-delay charge 44 and an ejection charge 45 such that the upper stage engine can function to propel the upper stage for a period of time, followed by a coasting period corresponding to the burning time of the delay charge 44 and an ejection sequence corresponding to the ignition of the ejection charge 45 which is usually employed to separate a nose cone from the upper stage and possibly eject a parachute to lower the upper stage back to the earth. A retainer cap 46 is usually frictionally engaged Within the leading end 47 of an upper stage engine to retain the ejection charge, and which may also serve as a sort of protective wadding between the combustion products of the ejection charge 45 and the parachute or nose cone contained within the upper stage outer rocket body section above the ejection charge engine.

As will be apparent, in operation, our assembly functions as follows: The lowermost engine (illustratively engine A of FIG. 3) is ignited by some external means such as an electrical resistance wire element inserted upwardly within the cavity 39 into contact or close proximity to the propellant charge 38. As the propellant charge 38 burns from the discharge end 37 to the opposite end of the engine, combustion products will be forced downwardly through the nozzle 36 to provide thrust for the rocket. As the combustion of the propellant charge 38 proceeds to the leading end 38a of the charge, the hot combustion products, including gaseous products and small particles of the burning propellant charge 38, are emitted upwardly in the direciton of the arrow C and into the discharge end 34 of the next engine B to ignite the propellant charge 43 of the next stage.

As the combustion front breaks through the leading end 38a of the propellant charge 38, an intial pressure front or wave is formed which tends to force the adjacent ends 33 and 34 of the engines A and B apart. Part or all of the pressure is vented through the ports 32a and the engines A and B are held together by frictional engagement with the coupler 32 until the sharp and much greater pressure generated by the ignition of the propellant charge 43 forces them apart. In this way, the reliability of sequential ignition of the propellant charge 43 is materially improved to a point of almost being foolproof.

Having described our invention and the presently preferred embodiments thereof, we claim:

1. A model rocket engine assembly for multi-stage rockets, especially adapted to achieve reliable sequential ignition of the pyrotechnic model rocket engines contained within upper stages of said assembly, each said stage comprising:

(a) an outer cylindrical body casing and a pyrotechnic rocket engine disposed therewithin, each said engine comprising a heat-sensitive nozzle member at its lower end and a pyrotechnic charge located thereabove in pyrotechnic communication with said nozzle member and also in pyrotechnic communication with the pyrotechnic charge of the engine located next thereabove, each said nozzle member-pyrotechnic charge assembly being encased in a tubular engine shell to form an engine fixed within a respective stage body casing, each said engine disposed in end-to-end relationship within its respective body casing, the upper end of each of said engines being located within pyrotechnic igniting distance of the lower end of the next of said engines, such that hot combustion products emitted from the upper end of a preceding engine pass through the nozzle member of the next succeeding engine and ignite the pyrotechnic charge of the next succeeding one of said engines, and (b) an engine coupler member comprising an annular coupling sized to receive the adjacent ends of said tubular engine shells and to releasably hold said engine shells in said end-to-end adjacent relationship by frictional engagement, with the upper end of the lower of one of said engines located within pyrotechnic igniting distance of the lower end of the engine of the'next stage located next thereabove, said annular coupling including:

means defining apertures therein to vent the pressure front formed when a preceding one of said rocket engines burns to its upper end to delay separation of said stages until the pyrotechnic charge of the engine of said next succeeding stage is ignited by the hot combustion products emitted from the upper end of the engine located in the stage therebelow.

References Cited UNITED STATES PATENTS 3,190,221 6/1965 Gariboldi 102-494 3,262,266 7/1966 Howison 102-494 3,292,302 12/1966 Estes et al. 10234.S X

ROBERT F. STAHL, Primary Examiner US. Cl. X.R. 102-37], 49.4 

